Fixes issue #63
We can have edges connecting vertices on different parts of the domain boundary while lying in the interior. These were incorrectly flagged as DirichletBoundary by the general MeshInfo::deriveEdges() method.
This commit removes this method and replaces it by two specialised methods
- deriveEdgesForRectangles()
- deriveEdgesForFullAnnulus() which are employed by the corresponding mesh generation routines and placed in the respective source files.